1. Field of the Invention
The present invention relates to an optical isolator for use in an optical fiber communication system, an optical measurement system, and the like.
2. Description of the Related Art
In an optical fiber communication system in which a semiconductor laser is employed as a light source, in particular in an optical system which is implemented by high speed digital transmission method or analog direct modulation method, reflection noise which is generated when reflected light from optical connector connection points, optical circuit components and the like employed in the optical fiber circuit is made incident on the semiconductor laser again often causes serious problems in designing system and device. In such cases, for the purpose of removing the reflected light which is made incident on the laser again, an optical isolator is used. The basic function of the optical isolator is to transmit the light emitted from the semiconductor laser (the light source) to a transmission path such as optical fiber through the optical isolator without any losses, and at the same time to cut off the reflected light from the optical fiber and the like in order to prevent it from returning to the semiconductor laser (the light source).
The conventional optical isolator, in general, includes: a polarizer; an analyzer; and a magneto-optical member which has the Faraday effect (the magneto-optical effect) and is provided between the polarizer and the analyzer. The magneto-optical member has been constituted such that magnetic substance and dielectric substance are laminated in the form of thin film with irregular thickness given to each layer; or that two dielectric multilayer films in each of which magnetic substance and dielectric substance are alternately laminated with regular thickness and an irregular lamination portion are formed in the form of thin film. And, for the polarizer and the analyzer, Rochon prism made of calcite, rutile single crystal in the form of wedge, polarizing beam splitter (PBS) or the like has been employed.
Now, since the above-mentioned Rochon prism made of calcite or the rutile single crystal in the form of wedge which is employed as the polarizer and the analyzer uses optical crystal, its external dimension becomes inevitably large. And, for the polarizing beam splitter, dielectric multiplayer film needs to be formed on the slant face of triangular prism in which glass substrate is employed as base material, forcing its external dimension to become large.
In the light of the foregoing, the present invention was made in order to solve the above-mentioned problems associated with the prior art, and therefore has an object to provide an optical isolator with a compact dimension.
According to one aspect of the present invention, there is provided an optical isolator including: a polarizer for taking out polarizing component from incident light; an analyzer which is used in combination with the polarizer; and a magneto-optical member which is formed in the form of thin film and provided between the polarizer and the analyzer, wherein the polarizer and/or the analyzer are/is composed of magnetic substance cluster thin film and are/is formed integrally with the magneto-optical member.
According to another aspect of the present invention, there is provided an optical isolator according to the first aspect, wherein the magnetic substance cluster thin film is made of cobalt minute particle cluster.